la. Ribbons inseparable, cells tightly joined, bilabiate process marginal 2
lb. Ribbons separable, cells loosely joined, bilabiate process central
B. yucatanensis von Stosch
2a. Ribbons usually straight, cells biangular, triangular, or quadrangular, intercellular spaces drop shaped, open only near elevations, costae interrupted in valve center
B. malleus (Brightwell) Van Heurck emend, von Stosch
2b. Ribbons curved in transapical plane, or straight or nearly straight, cells biangular (quadrangular?), intercellular spaces dumbbell shaped, costae partly continuous B. horologicalis von Stosch
B. horologicalis—known from Florida (Gulf of Mexico) and Melville Bay, Australia.
B. malleus—known with certainty only from the North Sea, the English Channel, the French and Portuguese Atlantic coasts, Portuguese Guinea, and Leigh, New Zealand.
B. yucatanensis—known from Australia and the type locality, Porto Progreso, Yucatan. How to identify: The species are distinguished mainly by the shape of the ribbons and may thus be identified in water mounts. Details of valve structure may be recognized by phase contrast examination of material cleaned of organic matter as air mounts (von Stosch, 1977, 1987) or mounted in a medium of a high refractive index.
Remarks: The information on distribution is from von Stosch (1977, 1987), who emphasized that all three species might have been identified as B. malleus in the past. Bellerochea yucatanensis is characterized by the loosely connected cells in ribbons implying that only single valves will be present in cleaned material. The two other species occur mostly as pairs connected by the filaments of the marginal ridges (except for terminal valves). In valve view B. malleus differs from B. horologicalis by the median part of the valve being without costae and by an unevenly ribbed marginal ridge. Von Stosch (1986) described B. horologicalis var. recta from Townsville, north Queensland, Australia, as distinguishable from the nominate variety by having straight or nearly straight chains.
Genus Ditylum J. W. Bailey ex L. W. Bailey 1861 (Plate 48, Table 58) Lectotype: Ditylum trigonum J. W. Bailey ex L. W. Bailey (vide Round et al., 1990, pp. 292 and 689).
Correct name: Ditylum brightwellii (West) Grunow (vide Van Heurck, 1880-1885, plate 114).
References: West, 1860, p. 149, Plate 7, Figs. 6a and 6b; Bailey, 1861, p. 332, Plate 7; Van Heurck, 1880-1885, Plate 114, Figs. 3-9, Plate 115, Figs. 1 and 2; Schröder, 1906, p. 355, Fig. 24; Hustedt, 1930, p. 784, Figs. 457-460; Cupp, 1943, p. 148, Fig. 107; Hendey, 1964, p. Ill, Plate 5, Fig. 1; Drebes, 1974, p. 59, Fig. 44; Hasle, 1975, Figs. 144-148; Hargraves, 1982; von Stosch, 1987, p. 57, Figs. 112-203; Takano, 1990, pp. 296-297; Delgado & Fortuflo, 1991, Plate 60, Figs, b, c, and d.
Generic characters: Cells solitary.
Cells in girdle view rectangular. Cells in valve view usually triangular.
Marginal ridge fimbriate (with ansulae) or slotted (a basal membrane with entire margin but perforated by evenly spaced pervalvar slots).
Valve structure consisting of radially arranged poroid areolae and/or ribs starting from a nonperforated area around a central bilabiate process. External part of process long. Chloroplasts numerous small granules.
TABLE 58 Morphometric Data of Ditylum spp.
Pervalvar axis ((Am)
Valve areolae or ribs
Mantle areolae in 10 (im
D. brightwellii 80-130
D. buchananii 52-112
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